INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

Related Words

Relevance

Dissimilar Words

Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious Duckworth also faced backlash from critics who argued that her message was, at best, a series of hollow exhortations to simply try harder and, at worst, an insidious form of victim-blaming that ignored structural inequality. — Meghan O’Gieblyn, New Yorker, 14 Sep. 2026 If anything, this makes those insidious Fridays insignificantly safer than the state average for the period. — Mike McRae 08, New Atlas, 8 Sep. 2026 Growing up in Beverly, Frates – the warrior against ALS who succumbed to the insidious disease in 2019 – was a huge fan of the Bruins’ star and had a poster of the defenseman in his room. — Steve Conroy, Boston Herald, 6 Sep. 2026 But the insidious harm that moves in the other direction — from illness, through a patient, into the person treating her — has no forum at all. — Jennifer Adaeze Okwerekwu, STAT, 1 Sep. 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

That will, ultimately, get us through even this treacherous moment.

— Jim Cramer, CNBC, 15 Oct. 2026
But the terrain is treacherous with muddy roads and slippery rocks.

— Paula Wethington, CBS News, 14 Oct. 2026

Definition of treacherous

Adjective

Coleman said each design has its own distinct character and can be styled individually, either as a subtle everyday detail or a sculptural statement.

— Tianwei Zhang, Footwear News, 15 Oct. 2026
As the researchers saw, introducing random mutation could still make subtle structural tweaks that produced enzymes that were considerably more active.

— ArsTechnica, ArsTechnica, 14 Oct. 2026

Definition of subtle

Adjective

The Idaho Consumer Protection Act, enacted in 1971, protects consumers from false, deceptive or misleading representations, advertising, pricing and contracts.

— Harllie Stevenson, Idaho Statesman, 14 Oct. 2026
What Apple says about suspicious iMessages Apple says this type of deceptive messaging uses social engineering, a tactic in which scammers rely on impersonation and manipulation to persuade people to share personal information.

— Kurt Knutsson, FOXNews.com, 13 Oct. 2026

Definition of deceptive

Adjective

Screening mammograms miss about one in eight breast cancers overall, and people with dense breasts are more likely to get false-negative results, the American Cancer Society reports.

— Samantha Agate, Kansas City Star, 14 Oct. 2026
Overall, screening mammograms miss about one in eight breast cancers, and people with dense breasts are more likely to get false-negative results.

— Samantha Agate, Charlotte Observer, 14 Oct. 2026

Definition of false

Adjective

As a result, choosing a plan based solely on monthly premiums can be misleading.

— Cindy Krischer Goodman, Sun Sentinel, 14 Oct. 2026
The Idaho Consumer Protection Act, enacted in 1971, protects consumers from false, deceptive or misleading representations, advertising, pricing and contracts.

— Harllie Stevenson, Idaho Statesman, 14 Oct. 2026

Definition of misleading

Adjective

Hanuman inspires him to avenge the rape of his mother by a corrupt policeman working for a deceitful Hindu nationalist spiritual leader.

— Sohini Sarah Pillai, The Conversation, 14 Oct. 2026
Magpies are opportunistic scavengers, incredibly cunning and deceitful and capable of calculated deception.

— Voice of the People, New York Daily News, 28 Sep. 2026

Definition of deceitful

Adjective

What prevents an incorrect action from propagating into the physical process?

— Gregory Shahnovsky, Forbes.com, 13 Oct. 2026
The sports media rarely treats athletes who espouse liberal or progressive political views as problematic, even when those views are provocative, divisive, or factually incorrect.

— Bobby Burack OutKick, FOXNews.com, 8 Oct. 2026

Definition of incorrect

Browse Nearby Words

inside tracks

insidious

insidiously

See all Nearby Words

Articles Related to insidious

Cite this Entry

Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 16 Oct. 2026.

Copy Citation

Synonyms of insidious

adjective

Example Sentences

Browse Nearby Words

Words of the Year: A Decade in Review

Red Carpet Words: Our Top 7...

2014 Word of the Year: Culture

Cite this Entry

More from Merriam-Webster

Word of the Day

zenith

Popular in Grammar & Usage

'Affect' vs. 'Effect'

Merriam-Webster’s Great Big List of Words You Love to Hate

The Exceptions of '-s' and '-es' Plurals

Is it 'nerve-racking' or 'nerve-wracking'?

What's the difference between 'fascism' and 'socialism'?

Popular in Wordplay

16 Food Words Recently Added to the Dictionary

The Real Origin of 'Supercalifragilistic'

9 Words That Sound Like Insults But Aren't

7 Words for Bad Endings and Rough Situations

The Words of the Week - Oct. 16

Popular

'Affect' vs. 'Effect'

16 Food Words Recently Added to the Dictionary

The Real Origin of 'Supercalifragilistic'

Games & Quizzes